DESCRIPTION: (Adapted from the applicant's Description) The goal of this study is to develop analytical methods that can be applied to estimate in utero exposures of children to manganese (Mn) in deciduous human teeth. The biomarker using tooth histology may be applied to cross-sectional and longitudinal studies of synchronous relationships between prenatal Mn exposure and brain development. In Experiment 1 rats will be exposed to equal amounts of Mn by three routes to identify target tissues for Mn accumulation. In Experiment 2 rats will be injected with Mn during organogenesis, limb development, and bone maturation. In Experiment 3 the investigator will use stable enriched isotope and radioisotope labeling to study histological cross-sections of rat brains and tooth enamels. The methods to be developed and validated in this pilot study can be applied to evaluating prenatal and early postnatal Mn exposures of human children associated with violence, aggression, ADHD, and learning disabilities using shed deciduous human teeth.